Stream Temperature Variability: Why It Matters

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United States Department of Agriculture
RT
MENT OF AGRI C U L
PNW
Forest Service
Pacific Northwest
Research Station
I nsi d e
A Short Primer on the Chinook
Salmon Lifecycle................................................2
Beyond Degree Days...........................................3
In the Lab...........................................................3
Genetic Influences...............................................4
New Information for Future Planning..............5
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issue one hundred sixty three / july 2014
“Science affects the way we think together.”
Lewis Thomas
Abby Tillotson
Stream Temperature Variability: Why It Matters to Salmon
Stream temperature can affect development of Chinook salmon. The five salmon fry above are from
the same family and emerged on the same day, but, as eggs, were exposed to different temperature
treatments.
“Variability is the law of life.”
H
—William Osler
igh in the mountains, winter’s deep
snow melts and becomes an icy
stream that gushes down the mountainside. As the weeks go by, the water’s journey downhill continues. It backs up around
large boulders, logs, and banks, creating
warmer, shallow pools in some places, cooler
and deeper pools in others.
Eventually, the raging torrent calms, widens,
flattens, and warms, tripping more delicately
over rocks in dappled sunshine. The seasons
progress, and the stream continues to traverse
long and winding miles toward the ocean. It
flows under bridges, next to roads and highways, over dams, past vacation homes and
campgrounds, and through agricultural areas,
small towns, and large cities. Everything it
encounters has the potential to affect its
temperature.
I N
S U M M A R Y
Salmon evolved in natural river systems,
where temperatures fluctuate daily,
weekly, seasonally, and all along a
stream’s path—from the mountains to
the sea. Climate change and human
activities alter this natural variability.
Dams, for example, tend to reduce
thermal fluctuations.
Currently, scientists gauge habitat
suitability for aquatic species by
establishing minimum/maximum
temperature thresholds and relying on
mean temperature readings to establish
management priorities. But temperature
effects on salmon are more complex. A
new study demonstrates that temperature
variability can affect emergence timing
in Chinook salmon, potentially altering
predictions about how these fish may
respond to a changing climate. It
also reveals that genetics can make a
difference in how an individual responds
to stream temperature variance.
The study indicates that the commonly
used degree-day accumulation model is
not sufficient to predict how organisms
respond to stream temperature. Changes
in how the degree days are delivered
have the potential to alter the timing of
life history transitions in Chinook salmon
and other organisms. Emerging from
the gravel a few days earlier or later
could directly affect their survival due
to changes in available food resources,
competition for feeding grounds, or
strong currents.
Meanwhile, aquatic species are subject to
and absolutely dependent on the landscape
and water features in which they evolved,
including the stream’s fluctuating temperature patterns. Researchers have known this
for decades, but human activities and climate
change have made it critical to more fully
understand what makes good habitat for individual species.
Water temperature was long ago identified as
a key predictor of survivability for fish, and
this is particularly true for salmon. In recent
years, scientists have looked at mean water
temperatures in rivers and streams to measure
habitat suitability. Because overly warm water
can be lethal for fish, scientists also have been
concerned about abnormally high temperatures. A new study, however, shows that relying on only mean and extreme temperatures
without regard for how temperatures change
throughout a day, season, or year may oversimplify the picture of what aquatic species
need to thrive.
Ashley Steel, a statistician and quantitative researcher with the Pacific Northwest
Research Station, recently teamed with
Brian Beckman, a fisheries biologist with
the National Oceanic and Atmospheric
KEY FINDINGS
• Early Chinook salmon life stages can be altered—with potential long-term biological
and ecological consequences—by stream temperature variations, even when the daily
mean temperature remains relatively unchanged and fluctuations are within established
thresholds.
• Emergence timing in Chinook salmon could be changed by nearly a week simply as a
result of changes in temperature fluctuations.
• Traditional degree-day accumulation models alone are insufficient to predict stream
temperature suitability for aquatic species. Decisionmaking about habitat suitability
and future species distributions are likely incomplete when managers consider only
mean or maximum temperatures.
• Genetic differences most likely will contribute to whether and how an individual
salmon responds to altered stream temperature variations.
Administration, and other researchers to try
to understand how thermal variability at daily
and seasonal scales might affect salmon emergence, growth, and development. They also
wondered whether individuals within the same
stock, representing various genetic lineages,
would respond similarly to altered thermal
patterns.
A SHORT PR I M ER ON TH E CHI NOOK SA LMON
LI FECYCLE
C
hinook salmon generally spawn in
the fall in gravel-bottomed rivers,
depositing their eggs deep in the
loose rocks. Tiny black spots—the developing
eyes—appear on the eggs several weeks later,
and scientists refer to this life stage as eyed
eggs.
Out of the approximately 4,000 eggs a female
lays, only a few salmon survive to adulthood.
Survivors attempt to return to their native
river and migrate upstream to spawn. After
spawning, Chinook salmon die and become
food for bears, raccoons, coyotes,
weasels, eagles, and other forest
creatures.
Jon Dickey
After hatching, the young alevin remain in
their pebbly nest, using their yolk sacs for
nutrition. In four to six weeks they fully
absorb the sacs and become fry. The tiny fry
wriggle up out of the gravel, and when they
are large enough to feed on insects, they are
called parr.
Parr spend three to 15 months in the river
channel, hopefully learning to avoid predators while building the strength and stamina
they need to survive the transition from river
to ocean living. When they go through physiological changes allowing them to live in saltwater, they transform into smolts and swim
into the ocean, where they live and feed for
several years.
Salmon are cold-blooded, which means all of their biological processes are controlled by temperature. Above, an adult
salmon in the Tye River, Wash.
This complex lifecycle requires
specific habitat conditions across
entire stream networks and
throughout the seasons of the year.
The salmon’s well-timed physiological and behavioral development depends on specific chemical
reactions.
“Salmon are cold-blooded, which
means all their biological processes are absolutely controlled by
The overarching goal of the study was to
determine whether ecologists, planners, and
managers should consider past and predicted
changes in thermal variability in addition to
optimal minimum, maximum, and mean temperatures in their conservation and management plans.
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temperature,” says Beckman. “So we know
that if temperatures change, there will be biological consequences. One thing that makes
this particularly relevant for Chinook salmon
is that they spend a lot of time in the juvenile
stage in freshwater.”
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n recent decades, land managers have
used “degree days” to measure water
temperature. The degree-day accumulation method is based on the understanding
that organisms require a certain amount of
accumulated heat to develop correctly. Using
this method, scientists can quantify how much
thermal energy an individual has received.
Steel explains: “If the water temperature is 10°
for one day, the egg accumulates 10 degreedays. If it’s exposed to 5° water for two days,
it also accumulates 10 degree-days. Chinook
salmon, for example, need approximately
1,100 to 1,200 degree-days to go from fertilized egg to emergence. Scientists thought that
it didn’t particularly matter how those degrees
were distributed—4° for a day, 6° for a day, 4°
for a day, 6° for a day would still be 20 degreedays over four days. Five degrees for all four
days would also come out to 20 degree-days.”
patterns while delivering approximately the
same number of degree days.
“We were interested in looking at the complexity of water temperature and trying to
understand whether there were biological
consequences from that complexity,” says
Steel. “The relationships are not simple,
but we have traditionally simplified them
because we could only go out and measure
the water temperature in one place at one
time—that’s the data we had.”
Measuring methods developed over the past
few decades have enabled scientists to more
closely track water temperatures. “We have
tiny water-temperature measuring devices
that are about the size of a quarter, but a bit
thicker,” says Steel. “They’re not terribly
expensive, so we can put them in different
parts of the river network and have a much
more complete picture of what a river water
temperature regime really looks like. They can
record water temperature every minute, every
hour, every day.”
Karrie Hanson
BEYOND DEGREE DAYS
Existing research shows that extreme changes
in temperature cause physiological stress in
fish, but Steel and Beckman’s project is the
first to specifically explore different scenarios for degree-day accumulation within
natural temperature ranges. The team wanted
to find out if any biological consequences
can be expected in terms of length, weight,
emergence timing, or condition at emergence
when water temperatures fluctuate in various
T
o test the effects of various thermal patterns on the early life stages
of Chinook salmon, the research
team reared eyed eggs from the Cle Elum
Supplementation and Research Hatchery
on the Yakima River in Washington. They
placed eggs from eight different genetic lines
in emergence chambers designed to mimic
a river bottom, and created eight water temperature regimes. They reared a set of eggs
from each set of parents in each of the eight
thermal regimes, for a total of 64 emergence
chambers.
Karrie Hanson
I N TH E LA B
Fairly soon after entering the chambers, the
eggs began hatching. Over a period of weeks
and months, the alevin reached the fry stage
and began emerging into a second chamber.
Each day, the team recorded the size, length,
weight, condition, and state of development of
the emerging fish.
Of the eight temperature regimes to which the
eyed eggs and alevin were exposed, all were
within optimal temperature thresholds for
salmon, but differed in how the degree days
were accumulated. Two were kept at a relatively stable 41 °F throughout the experiment.
A stream’s temperature tends to fluctuate over time: between seasons and also within a 24-hour period.
Water temperature in a river system also changes over space, influenced by upwelling of groundwater,
amount of shade, type of stream bed, and incoming flows. The water temperature in this side channel,
for example, was less variable than in the main stem of the Sauk River, Wash.
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temperature regimes,” says Steel. “It suggests
that some genetic groups or individuals could
be at greater risk, and others may be able to
adapt to changing water temperature regimes.
There could be strong management uses for
that kind of information.”
“This finding suggests that there are some
genetic differences in how responsive particular populations might be to changes in water
The study’s sample eggs were all from the
same hatchery, and Steel conjectures that
even larger differences might be seen among
populations from different river systems. “Our
eggs were all very similar, and yet we still saw
some pretty strong differences in how they
reacted to our experimental water temperature
patterns,” she says.
ne of the study’s significant findings was that the eight family groups
didn’t all react to water temperature
fluctuations the same way. The emergence
timing of some family groups was strongly
influenced by temperature variances. Other
family groups emerged after a set number of
degree days no matter what occurred with the
water temperature.
Jon Dickey
Abby Tillotson
GEN ETIC I N FLU ENCES
The researchers placed eggs from eight genetic
lines in emergence chambers where they were
exposed to eight water temperature regimes, all
within the optimal temperature threshold for
salmon but differing in how degree days were
accumulated.
As an example of other regimes the scientists
employed, one chamber reduced the temperature by about 2 degrees each week to isolate
seasonal patterns found in natural rivers.
Another fluctuated temperatures by 9 degrees
daily, alternating between 41 °F at night and
50 °F during the day to isolate daily fluctuations that are found in almost all naturally
flowing rivers. The researchers also tested
abnormal patterns.
The findings suggest there may be genetic differences in how responsive particular salmon populations
are to changes in water temperature regimes.
Abby Tillotson
No differences in length, weight, or condition
could be attributed to the different thermal
regimes and those exposed to more normal
patterns of daily variations, but the total number of degree days required before emergence
did vary.
“Those fish that experienced the two stable
regimes accumulated about the same number
of degree days that our rule of thumb would
predict,” says Steel. “But we found that fish
exposed to the very strange thermal regimes
accumulated a lot more degree days before
they emerged, and those exposed to daily variability or seasonal patterns, or daily plus seasonal variability emerged after accumulating
fewer degree days.”
The researchers concluded that how degree
days are delivered could affect a salmon’s
lifecycle. “Just by changing the variability of
the temperature pattern, even though we were
still delivering about the same amount of temperature every day or every couple of days,
we observed a difference in emergence timing
equivalent to about a week in a cool stream.
So traditional degree-day models aren’t sufficient to explain our results,” says Steel.
The experimental set up for testing the effects of temperature on early Chinook salmon life history.
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lthough Steel and Beckman are hesitant to extrapolate too much from the
results of their lab experiment, the
study builds on an established body of scientific wisdom and leads them to believe that
water temperature variability can affect the
phenology (the timing of biological events) of
aquatic species. Emergence timing, in particular, can be critical for salmon. It can make a
life-or-death difference if temperatures cause
the fry to emerge from their gravel nest a few
days too early or remain a few days too long.
“If they come out too early—say, in the
middle of February during a winter freshet—
they’re just going to get washed away downriver,” says Beckman. “The currents may be
too strong for the young fish to resist. If they
come out late, the stream may be crowded,
leaving no place for an individual to establish
its feeding territory. Food sources may not
be available or competition for available food
may be altered. So the idea is that there’s an
optimal timing for the juvenile salmon to
come out into the water column; if temperature regimes change, we could see higher
mortality and/or shifting patterns of mortality
(early versus late).”
L A N D M A NAG E M E N T I M PL ICAT ION S
• Decisionmakers often apply landscape models to identify freshwater management priorities for conservation and restoration planning and to predict future species distributions; incorporating stream temperature variability into calculations may improve these
models.
• Management decisions for hydropower operations, wetland mitigation, and riparian forest management can be improved by considering the natural temperature patterns in
their full complexity, rather than focusing only on lethal thresholds and total degree
days delivered within a given time period.
• Monitoring freshwater temperature is essential for managing fish and other aquatic
organisms. This study provides a rationale for collecting and archiving hourly information, instead of simply mean or maximum daily temperature.
• Fisheries management during a changing climate might be improved by considering
genetic predispositions that could lead to increased risk or resilience, particularly for
listed and endangered species.
Jon Dickey
N EW I N FOR M ATION
FOR FUT U R E
PLA N N I NG
Climate change, dams, irrigation, landscape
conversion, and other human activities can
lead to altered thermal patterns. Steel suggests that as scientists work toward greater
understanding of human impacts and climate
change on the lifecycle of aquatic species,
it might be prudent to include temperature
variability in their protocols and conceptual
models.
“It’s quite possible that there are effects of
the changing variability in water temperature
regimes, even when the means aren’t changing very much,” she says. “As scientists try to
estimate where species are going to be under
different climate conditions, our results suggest that they are going to want to think about
the whole thermal regime, not just the mean
temperature. It’s an additional management
tool for species at risk.”
“Water is life’s matter and matrix,
mother and medium.”
—Albert Szent-Gyorgyi
W R I T E R’ S P RO F I L E
Marie Oliver specializes in science writing and developmental editing. She can be
reached through her website at http://www.
claritywriting.com.
If salmon emerge from their gravel nests too early, water currents may be too strong for the young fish,
and food sources may not yet be available.
FOR FU RT H ER R EA DI NG
Steel, E.A.; Tillotson, A.; Larsen, D.A.;
Fullerton, A.H.; Denton, K.P.; Beckman,
B.R. 2012. Beyond the mean: the role
of variability in predicting ecological
impacts of stream temperature. Ecosphere.
3(11): art104. http://www.esajournals.org/
doi/pdf/10.1890/ES12-00255.1.
Steel, E.A.; Lange, I.A. 2007. Alteration of
water temperature regimes at multiple
scales: effects of multi-purpose dams
in the Willamette River basin. River
Research and Applications. 23: 351–359.
http://onlinelibrary.wiley.com/doi/10.1002/
rra.985/pdf.
Sowder, C.; Steel, E.A. 2012. A note on the
collection and cleaning of water temperature data. Water. 4: 597–606. http://www.
mdpi.com/2073-4441/4/3/597.
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sci e ntist profil e s
ASHLEY STEEL is a statistician and quantitative
researcher with the Pacific
Northwest Research Station
in Seattle, Washington,
who uses quantitative tools
to study rivers and watersheds. Her research has
focused on harnessing landscape-scale data
to predict in-river conditions, quantifying and
modeling complex water temperature regimes,
and performing sensitivity analyses to support
the best use of modeled data. She enjoys collaborating with other scientists to link ideas
and tools from aquatic ecology to research on
trees, wildlife, fire, and people.
Steel can be reached at:
USDA Forest Service
Pacific Northwest Research Station
400 N 34th St., Suite 201
Seattle, WA 98103
Phone: (206) 732-7823
E-mail: [email protected]
BRIAN BECKMAN is a fisheries biologist
with the National Oceanic and Atmospheric
Administration’s Northwest Fisheries Science
Center. He has extensive expertise and experience in evaluating growth, smolting, and early
male maturation of salmonids in laboratory,
hatchery, and field environments. He seeks
to elucidate how growth, and the endocrine
mechanisms controlling growth, interact to
vary the age and season at which smolting
occurs in Chinook salmon and how seasonal
growth rates influence the rates of early male
maturation. His studies document how variation in genetics and rearing environments
influence salmonid life history.
COLLABOR ATORS
Keith Denton, Aimee Fullerton, Don Larson,
and Abby Tillotson, National Oceanic and
Atmospheric Administration Northwest
Fisheries Science Center, Seattle, WA
Beckman can be reached at:
National Oceanic and Atmospheric
Administration
Northwest Fisheries Science Center
2725 Montlake Blvd. East
Seattle, WA 98112-2097 Phone: (206) 860-3461
E-mail: [email protected]
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